Bricks of fired clay, called “Monomur bricks”, or of cement, called “blocks”, with cellular structure, are widely used for the construction of walls, floors, partitions or other elements of buildings.
The cells of these bricks, which are usually empty, of variable sizes and various shapes, serve to increase the thermal insulation. The free spaces of these cells must, however, be small enough to limit thermal convection and their walls must be thin enough to limit the conduction effect while maintaining a minimum mechanical strength. The heat resistance induced by the empty space of these cells is, however, limited by the convection effect of the air within it. It is possible to limit this effect by producing bricks having a larger number of smaller cells, but production of these so-called “Monomur” bricks is more complex and the resultant advantage is often cancelled by the increase in the conduction effect owing to multiplication of the walls of said cells.
The French patent application published under number 2521197A1 discloses bricks of fired clay with cells filled “with a cellular material with high thermal insulation value”, such as “polyurethane foam, polystyrene foam, or any other fibrous materials (glass wool or rock wool) or divided materials (cork agglomerate)”. However, depending on circumstances, these materials:
(i) are flammable and/or emit toxic gases in case of fire,
(ii) are potentially hazardous compounds as they are ultimately classifiable in the category of the RCFs (Refractory Ceramic Fibers) requiring specific conditions for placement and then management of waste,
(iii) lose their insulating properties over time (settling of the packing),
(iv) or have several of the above drawbacks.
Moreover, in certain cases packing of the bricks is done in situ at the site, this constitutes an additional constraint and requires additional labor.
Document FR 2876400 discloses the use of hollow bricks filled “with an insulating material based on a loose porous product”. The packing material is based on expanded perlite or expanded vermiculite, in which starch is used as thickener. This patent application also mentions the use of other components such as colloidal silica used as adhesive, hydrophobic agents, or dispersed plastic. The drawback of this solution lies in the low mechanical durability of the agglomerates, with a risk of deterioration during transport and installation of the elements. Moreover, the structure has low cohesive power, which notably leads to risks of loss of material during piercing and cutting of the walls. Settling of the grains over several years eventually leads to an uncontrollable decrease in insulating value.
Document FR 2927623 discloses elements of construction of the fired clay brick type, packed with foamed lime. This porous material consists of a lime-cement mixture of 65 to 90 wt % relative to the weight of total dry matter, fibers, mineral fillers, a hardener and a foaming agent. The principle is to make the lime set with a foaming agent to create air bubbles, trap them during the reaction and thus obtain a porous structure. The drawback of this solution lies in the need to use synthetic chemicals to help the lime to harden in the form of a porous material. Among these chemicals we may mention foaming agents, gelling agents, setting accelerators, and hardeners. With this method it is difficult to control the microstructure of such a material after synthesis, in particular the pore size and distribution, the total porosity and the type of stacks. Such a structure has low mechanical durability, which limits the potential reduction in the number or thickness of walls of fired clay brick and leads to risks of degradation of the porous material during placement of the elements of construction. It should also be noted that the presence of organic compounds (hardener, foaming agent, etc.) in the process may increase the fire resistance risk and the toxicity of the fumes emitted.
Thus, a problem that arises is to supply a building brick that does not have the drawbacks mentioned above; in particular a brick having good mechanical strength, i.e. above 10 kg/cm2, and a very good insulating character, i.e. below 0.100 W/mK, preferably below 0.05 W/mK.